Data from: Phylogeny of Selaginellaceae: there is value in morphology after all!

PREMISE OF THE STUDY: The cosmopolitan lycophyte family Selaginellaceae, dating back to the Late Devonian–Early Carboniferous, is notorious for its many species with a seemingly undifferentiated gross morphology. This morphological stasis has for a long time hampered our understanding of the evolutionary history of the single genus Selaginella. Here we present a large-scale phylogenetic analysis of Selaginella, and based on the resulting phylogeny, we discuss morphological evolution in the group.

METHODS: We sampled about one-third of the approximately 750 recognized Selaginella species. Evolutionary relationships were inferred from both chloroplast (rbcL) and single-copy nuclear gene data (pgiC and SQD1) using a Bayesian inference approach. The morphology of the group was studied and important features mapped onto the phylogeny.

KEY RESULTS: We present an overall well-supported phylogeny of Selaginella, and the phylogenetic positions of some previously problematic taxa (i.e., S. sinensis and allies) are now resolved with strong support. We show that even though the evolution of most morphological characters involves reversals and/or parallelisms, several characters are phylogenetically informative. Seven major clades are identified, which each can be uniquely diagnosed by a suite of morphological features. There is value in morphology after all!

CONCLUSIONS: Our hypothesis of the evolutionary relationships of Selaginella is well founded based on DNA sequence data, as well as morphology, and is in line with previous findings. It will serve as a firm basis for further studies on Selaginella with respect to, e.g., the poorly known alpha taxonomy, as well as evolutionary questions such as historical biogeographic reconstructions.

1. 研究背景：
广布的石松科（Selaginellaceae）为石松类植物类群，起源可追溯至晚泥盆世-早石炭世。该科仅包含卷柏属（Selaginella）一个属，且以多数物种整体形态看似缺乏分化而闻名。这种形态停滞现象长期以来阻碍了学界对卷柏属演化历史的认知。本研究对卷柏属开展了大规模系统发育分析，并基于所得系统发育树探讨该类群的形态演化。

2. 研究方法：
本研究选取了约750个已正式确认的卷柏属物种中的三分之一作为研究材料。基于叶绿体基因（rbcL）与单拷贝核基因数据（pgiC及SQD1），采用贝叶斯推断法重建类群的演化关系。同时对该类群的形态特征开展研究，并将关键性状映射至系统发育树上。

3. 主要结果：
本研究构建了整体支持度优异的卷柏属系统发育树，部分此前分类存疑的类群（如中华卷柏S. sinensis及其近缘类群）的系统发育位置现已获得高支持度解析。研究表明，尽管多数形态性状的演化存在反转和/或平行演化现象，但仍有部分性状具备系统发育信息价值。本研究共识别出7个主要演化支，每个演化支均可通过一组独特的形态特征进行精准界定。形态学数据终究具有不可替代的应用价值！

4. 研究结论：
本研究提出的卷柏属演化关系假说，同时基于DNA序列数据与形态学数据，具备充分的科学依据，且与既往研究结果相符。该假说将为后续卷柏属相关研究提供坚实基础，例如针对尚不明晰的α分类学（alpha taxonomy）研究，以及历史生物地理学重建等演化生物学问题。